Transparent and translucent containers, such as beverage containers, are typically inspected prior to being populated with content (e.g., liquid) and made available to consumers. For example, during manufacture of transparent or translucent containers, defects may be introduced into sidewalls of the containers. A defect that may be found in transparent and translucent containers is conventionally categorized as being one of two types; an opaque defect or a transparent defect. Opaque defects are inclusions in sidewalls of containers, wherein such inclusions are not transparent. In other words, opaque defects block light from passing therethrough. Transparent defects are those that do not block light from passing therethrough. Exemplary transparent defects include blisters (air bubbles in sidewalls of containers), wash boards (a series of horizontal waves or folds on sidewalls of containers), and checks (fine and shallow defects).
Conventionally, inspection of sidewalls of transparent and translucent containers has been performed in two stages: a first stage to detect opaque defects; and a second stage to detect transparent defects. In both stages, monochromatic LED illumination and monochrome cameras are employed in connection with detecting the transparent defects. In the first inspection stage, a backlight monochromatically directs light uniformly through the sidewall of the container, and a monochrome camera captures an image of the sidewall of the container while the light passes through the sidewall. A computing system can identify an opaque defect in the sidewall of the container based upon the image, as the defect will be depicted in the image as a dark region therein. In the second inspection stage, a backlight monochromatically directs light through the sidewall of the container in a pattern (such as a series of horizontal or vertical stripes of light). In other words, the backlight monochromatically directs light non-uniformly through the sidewall of the container, and a camera captures an image of the sidewall of the container while the backlight emits light non-uniformly. A computing system can identify a transparent defect in the sidewall of the container based upon the image, as the sidewall of the container is formed of refractive material, thereby causing the transparent defect in the sidewall of the container to be distinguishable from non-defective regions in the sidewall. It can be ascertained, however, that in the second inspection stage opaque defects may not be readily identifiable, as the image captured in the second stage includes dark regions (e.g., corresponding to dark stripes in a striped pattern).
Requiring two separate inspection stages to detect the two types of defects introduces complexities into a container inspection system. For example, in some conventional container inspection systems, separate sets of cameras are employed—one set of cameras for each inspection stage. In another exemplary conventional approach, a backlight of a container inspection system must be controlled such that it strobes between uniform lighting and non-uniform (striped) lighting. In such an inspection system, a camera captures two separate images in a short amount of time: a first image that is used to detect opaque defects; and a second image that is used to detect transparent defects.